The present invention relates to optics and laser beam shaping and more particularly to a device for reshaping a laser beam to correspond to an aperture of a beam director or other optical device.
Most solid state and some chemical lasers produce laser beams that are substantially square or rectangular, and do not have a central region which is un-illuminated (e.g., central obscuration.) Such laser beams may be directed onto targets at a great distance using a beam director or similar optical device. Beam directors typically include a moveable spherical telescope with an output aperture that is circular with a circular central obscuration through which the laser beam may not be projected. Accordingly, the most desirable shape for a laser beam to be projected from such a beam director is a “donut” (annulus) shape with the same ratio of inner and outer diameters that corresponds to the usable output aperture of the beam director. With this beam configuration, the entire laser beam can be placed onto, and substantially entirely fill, the usable output aperture of the beam director. If the laser beam, after suitable geometric scaling with telescopes both internal and external to the beam director, projects outside of the beam director aperture or within the central obscuration, the beam should be trimmed or “clipped” on the outside and “cored” inside the periphery of the beam. Typically this is performed using mirrors that reflect the unwanted portion of the laser beam out of the propagation path of the laser beam, for example into a beam dump. The beam power to be projected by the beam director is thereby reduced. Similarly, if the laser beam does not completely fill the aperture of the beam director the beam will not be focused as effectively, reducing the intensity or brightness of the focused laser beam at the target. In either event the intensity of the laser beam at the target is diminished.